1. Field of the Invention
This invention relates to the field of four-wheel drive systems for motor vehicles. More particularly, the invention pertains to a device for drivably connecting an axle shaft and the wheels of a motor vehicle
2. Description of the Prior Art
The powertrain for a part-time, four-wheel drive motor vehicle includes a transfer case driven from an engine through a multiple-speed transmission. The transfer case includes a first output shaft continuously connected to a first set of drive wheels through an axle differential and two axleshafts driven from the differential output. The transfer case includes a second output that drives a second axle differential mechanism or disconnects the transfer case input from the second differential mechanism, depending on the engaged and disengaged state of a clutch located in the transfer case.
When operating in two-wheel drive mode, the set of drive wheels that is then disengaged from the transmission output shaft has no drive connection to the components of the powertrain located between the nondriven wheels and the engine. To provide this drive connection in a conventional powertrain, the wheels of the axle that are driven from the transfer case only in four-wheel drive mode are equipped with hub locks, which alternately connect and release the wheels and the axleshafts that are driven from the associated differential mechanism. Hub locks are usually engaged manually or can be engaged automatically, provided a suitable power source and actuation mechanism are available.
U.S. Pat. No. 4,341,281 describes another solution to the problem, in which only one of the split axles of the part-time axle assembly is disconnected from the output of the corresponding differential mechanism, usually one of the side double gears of an epicyclic differential mechanism. To produce this effect, an actuator, such as a vacuum motor or solenoid, moves a sliding coupler along the axleshaft in opposite axial directions alternately to engage and disengage a connection between a side bevel gear of the differential mechanism and the axleshaft. However, when a vacuum motor or solenoid is used in a driveline, it requires control logic, an electronic system usually in the form of a microprocessor for processing the logic, electronic memory for storing the logic, various sensors, and conditioning circuitry, and a power source to produce the desired connection and disconnection between the engine and part-time drive axle. An external source of power, such as a connection to the engine intake manifold in the case of a vacuum-actuated motor, or an electrical power supply in the case of a solenoid, is required. Systems of this kind involve substantial cost in providing the microprocessor and control logic, and additional complexity and cost in manufacturing and assembly,
It is desirable to minimize the cost and complexity of these items in a driveline that can be activated when four-wheel drive operation is desired and deactivated for two-wheel drive operation, provided these functions can occur automatically and reliably.